West Nile virus (WNV) is a virus that is spread by mosquitoes.
Most cases of WNV are not serious and many people have no symptoms.
In less than 1 in 100 people who are infected, WNV causes serious symptoms, such as inflammation of the:
- brain
- spinal cord
- tissues surrounding the brain and the spinal cord
See West Nile virus - symptoms for more information.
How is West Nile virus spread?
WNV is usually spread by a bite from an infected mosquito. Mosquitoes become infected when they feed on infected birds. They then spread the virus to humans and other animals when they bite.
It can also be spread through an organ transplant or blood transfusion, although this is rare.
There is evidence that WNV can be spread from a mother to her baby during pregnancy or through breast milk. This is also rare.
See West Nile virus - causes for more information.
How common is West Nile virus?
There have been no cases of WNV occurring in the UK in people who have not travelled abroad. There was one UK case of WNV in 2006 and one in 2007, both in people who had visited Canada.
In 2010, there were 981 cases of WNV in North America.
Outlook
In around four out of five people, WNV will cause no symptoms. Other people may have mild flu-like symptoms that last a few days, such as a headache and high temperature.
If WNV develops into a severe condition, it can be fatal. Estimates of fatality rates are around 3-15 people in every 100 with a severe case of WNV. It is more likely to be fatal in elderly people.
